Ever since you were born the world is constantly changing, not just through big events but in smaller ways too.
The person you were born as no longer exists, at some point “you” died and you didn’t notice.
The world you live in does not even exist. There might be one objective reality, but none of us where ever there. Everything you experience is filtered and distorted by your past experiences and current beliefs.
The phrase of something being a lifetime ago exists for a reason.
You’re changing mentally and physically all the time, especially when you’re younger and going through so many phases of growing up.
String enough of those changes together and at some point you will effectively become a new person, only connected to the previous iterations by memories that you share.
The death of one interation and the beginning of another is bound to be a blurry mess, but you can see it clearly over a large enough span of time.
The same is true with the environment around you, and even the wider world. It goes through iterations just the same as we do because nothing stands still, even if we want it to.
Not only that. You no longer exist. As you were at birth, that is. And after some amount of time every so often in your life, you will continue to be unrecognizable to the version of you from x years in the past. Your cells die off and new cells are created until you are literally composed of different matter than you once were. The closest thing to a constant thing tying you together would be the electrical signals in your brain. Memories. Like computer code sent from one PC to another. Also the DNA determining how your body is built.
It’s the classic Ship of Thesseus problem. If you replace a ship’s parts one piece at a time over many years until the old parts of the ship no longer remain, is it still the same ship? And in the same way, are you still the same you? Maybe our lives are full of many different people tied together only by our thoughts, memories, and genetic code.
The neurons you’re born with stay with you for the most part. Most of their complex organization is formed through a series of one time events early in development that can’t really be replicated and then stays with you for the rest of your life. You get shingles when you’re older because the same neurons were with you that got infected by chicken pox when you were younger are still there. There’s a few limited areas in the nervous system where new neurons might be formed, but in general neurons are life long cells so be nice to your nervous system. Most other cell types in your body are turning over as you said, including glia and other types of cells in your brain.
In the UK we call this the “Trigger’s broom” problem: https://www.youtube.com/watch?v=56yN2zHtofM
At some point in the future, everyone who is currently alive, will be dead and the earth will be populated with people who do not exist yet.
Since I was born when my parent were in their late 30’s. And my father was as well, so my paternal grandfather was born in the 1890’s. When I was a kid he told me stories of his childhood. I was only 9 when he died, and at the time his stories were just that; stories. Now (I’m in my 50’s) I wish I had asked him things about those times. He was born and grew up in a world (mostly) without electricity, and without cars, phones, etc.
He was someone from a totally different world, and I knew him.
Added later: He was born “only” 129 years ago, everyone alive then, is now dead.
